1. Field of the Invention
The present invention relates to a device which is used in a single crystal production apparatus based upon Czochralski method and which is capable of measuring offset of the position of a crystal lifting wire from an expected position.
2. Description of the Related Art
In general, an apparatus for producing a single crystal based upon Czochralski method employs a wire or a shaft for lifting a grown single crystal. In order to reduce the overall height of the apparatus, a wire is preferably used rather than a shaft. The crystal lifting wire is suspended from an upper portion of the apparatus down to a rotary crucible containing a melt of the crystal's raw material. If the center axis of the crystal lifting wire is offset from the axis of rotation of the crucible, the growing crystal receives a force of appreciable level in the direction of crucible rotation from the melt surface so that the axis of rotation of the growing crystal is abnormally oscillated by the force, with the result that the the crystal does not grow in a cylindrical form and the growth cannot be continued.
Offset of the center axis of the crystal lifting wire from the axis of rotation of the crucible inevitably occurs due to, for example, a mechanical distortion of the crystal production apparatus or relative change in the constructive positions during a long use thereof, even though the lifting wire is initially set in axial alignment with the crucible, when the apparatus is newly installed.
It is therefore necessary that a periodical readjustment has to be conducted so as to reduce this offset to zero during use of the single crystal production apparatus, not to mention the adjustment at the time of the initial setting.
Unfortunately, no specific consideration has been given to this problem, and the readjustment has been conducted with the help of a naked eye without usage of any special measurement of the offset amount, so that an impractically long time is required for the centering of the lifting wire and the accuracy of the centering was not realized to be so high.